The overall goal of this proposal is to investigate interactions and relationships between sites and modes of electrical stimulation of the auditory system in a typical post-lingually deaf clinical population. Sites of stimulation will include the promontory, transcochlear lateral wall and the scala tympani. Types of stimulation include square wave electrical stimulation, speech, and tone-burst stimulation. Stimuli will be delivered electrically or acoustically and transduced from acoustical to electrical stimulation by the speech processor of the cochlear implant. Modes of intrascalar stimulation include monopolar and bipolar stimulation. Subject performance will be evaluated behaviorally and electrophysiologically. Wherever possible, identical stimulus and response paradigms will be used for extra- and intracochlear stimulation. In addition to the promontory versus scala tympani comparison, the predictive values of detection thresholds, cognitive evoked potentials, and pre- operative speech recognition abilities on post-operative speech recognition will be investigated. We hypothesize that pre- and post- operative thresholds and pre- and post-operative cognitive evoked potentials will be predictive of post-operative speech recognition abilities with a cochlear implant. We will also investigate the effects of five different electrode configurations on speech recognition with a cochlear implant. Variations of electrode configuration will include monopolar intrascalar stimulation that may result in lower operating current levels; the standard bipolar intrascalar stimulation of the Cochlear Corporation device, monopolar stimulation where an extrascalar electrode placed over the apical turn serves as the indifferent electrode; and the restriction of intrascalar stimulation to the basal half of the electrode array in two monopolar modes to mimic partial insertion in an ossified cochlea. These studies will supplement the information obtained previously, with the activation of 10 basal electrodes, including the roles of place and mode of stimulation in determining speech recognition abilities with a cochlear implant. The results of these studies may contribute to the design of safer cochlear implants if it is determined that comparable speech recognition skills are present with monopolar and bipolar modes of stimulation.